1. Field of the Invention
This invention relates to a non-skid, radar absorbing system disposed up on a substrate, its method of making, and a method of using the system.
2. Background Art
Radar absorbing materials (RAMs) are extensively used in various military applications, including stealth technology. They typically are coatings or bulk materials, the electrical and magnetic properties of which have been altered to allow the absorption of microwave energy at discrete or broadband frequencies.
Initial work on producing practical microwave absorbers predates World War II. Early efforts sought to reduce the detectability of a target, of which its radar cross-section (RCS) is a measure. Two types of materials were developed for this purpose. The first was a tuned-frequency, magnetically loaded rubber sheet (Wesch material). The second was a multi-layered material which was relatively thick (Jaumann absorber). It was formed from resistive sheets and low-dielectric plastic spacers.
Over the years, a search has been underway for RAMs that can be used on the surfaces of military targets to prevent them from being detected, located, or recognized by radar over a broad (2-100 GHz) radiation spectrum. But utilization of conventional RAMs generally requires thick applications, particularly at low frequencies. Such an approach creates bulkiness and difficulty in transportation and deployment. Further information about related considerations involving RAMs is found in K. J. Vinoy et al., xe2x80x9cRADAR ABSORBING MATERIALS,xe2x80x9d Kluwer Academic Publishers (1996), which is incorporated by reference.
Another obstacle to the development of satisfactory RAMs has been the effect on radar absorption and reflectance of applying a non-skid coating to the RAM. This is because non-skid materials typically are aggregates that are heterogeneous and have electromagnetic characteristics that are incompatible with RAMs. As a result, the retro reflectance characteristics of RAM may become dramatically altered by the presence of a non-skid layer upon which microwaves impinge. A non-skid coating, however, is necessary for operational field use, particularly under conditions of moisture and motion, in order to provide a safe foot hold for military personnel.
To some extent, the electromagnetic characteristics of the RAM and the non-skid layer are also modified when a protective environmental coating is applied to the non-skid layer.
Prior art references noted during an investigation in connection with the present invention include these U.S. Pat. Nos.: 4,606,848 Bond; 5,552,455 Schuler et al.; 5,844,523 Brennan et al.; 5,892,476 Gindrup et al.; and 5,900,097 Brown.
It is an object of the invention to provide a non-slip or non-skid radar absorbing material (RAM) which will overcome the above and other disadvantages.
More specifically, an object of the invention is to provide a RAM system including a radar absorbing layer, a non-skid matrix layer disposed adjacent thereto, and an optional protective environmental coating applied to the non-skid layer. The RAM system is used on a substrate, often having a non-planar or complex topography. The substrate is representative of the surfaces of military hardware or equipment. Ideally, the overall bulkiness and weight of the system minimize their detrimental effects on the substrate to which the system is applied.
A further object of the invention is to provide a non-skid, RAM system which is capable of both absorbing and scattering incident microwave radiation over a wide spectrum of incident microwave energy, including microwave (2-20 GHz) and millimeter wavelengths (20-100 GHz) frequencies.
A still further objective of the invention is to provide a non-skid, RAM system that includes a protective environmental coating, where the system retains the desired radar attenuating characteristics.
Another object of the invention is to provide methods of making and using a RAM system that can be applied to a non-planar substrate so that the thickness of the system can be controlled within acceptable tolerance limits.
In carrying out the above objects, the non-skid, radar absorbing system of the invention includes a radar absorbing material (RAM) layer juxtaposed with a surface of the hardware or equipment to which the system is applied or affixed. A non-skid matrix layer is disposed adjacent the absorbing layer. Optionally, a protective environmental coating is applied to the non-skid layer. The layers and the topcoat form a radar absorbing system that has electrical and magnetic characteristics that enable microwave energy at discrete or broadband frequencies to be at least partially absorbed.
In one preferred embodiment of the radar absorbing system, the non-skid matrix layer comprises microballoons that alter the dielectric properties of the non-skid coating with minimal added weight.
Another embodiment of the non-skid RAM calls for the non-skid matrix layer to include less than about 5 volume percent of carbon fibers to imbue the system with changed electrical and magnetic properties with minimal further change in weight or volume. If desired, carbon fibers can be added to the non-skid matrix layer, the fibers having an average ratio of length to diameter between about 20 to about 40.
In yet another preferred embodiment, the non-skid matrix layer includes a non-skid additive selected from the group consisting of silicon dioxide, pumice, quartz, aluminum, aluminum oxide, other ceramics, crushed walnuts and mixtures thereof.
In another preferred embodiment of this system, the non-skid RAM is covered with a chemical agent-resisting coating (CARC) as the environmental coating.
Still further preferred modes of practicing the invention include its method of making and use.
The objects, features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.